Circuit breaker distribution system configured to provide selective coordination

ABSTRACT

A circuit breaker distribution system is configured to provide selective coordination. The system comprises a solid-state switch disposed as a main or upstream breaker and a switch with an over current protection disposed as a branch or downstream breaker. The solid-state switch comprises a microcontroller including a processor and a memory, and computer-readable logic code stored in the memory which, when executed by the processor, causes the microcontroller to: allow repeated pulses of current through to the branch or downstream breaker in an event of an overload or short circuit, and choose a maximum current limit for the solid-state switch as a “chop level” such that the chop level is chosen higher than a rated current of the solid-state circuit breaker but low enough that the solid-state switch is not damaged from repeated pulses over a period of time needed to switch OFF the branch or downstream breaker.

BACKGROUND 1. Field

Aspects of the present invention generally relate to a circuit breakerdistribution system configured to provide selective coordination.

2. Description of the Related Art

The problem is how to achieve selective coordination in an electricaldistribution system when the main or upstream circuit breaker is asolid-state circuit breaker (SSCB) and the branch or downstream breakeris a conventional thermal/magnetic circuit breaker.

The field of invention is electrical distribution systems for switchinglow voltage (<=1000V) power circuits in residential, industrial andcommercial buildings. These systems utilize circuit breakers which arearranged in a hierarchical manner. Typically, a larger main circuitbreaker feeds power to multiple smaller branch breakers. These branchbreakers feed power to either end loads or to further smaller branchbreakers. The main breaker is said to be “upstream” of the branchbreakers, and the branch breakers are said to be “downstream” of thedevices that feed power to them. Likewise, a branch breaker is upstreamof any smaller breakers to which it feeds power. The upstream breakerstypically are designed with short circuit interruption ratings thatmatch or exceed the downstream breakers. In this way, the upstreambreakers provide backup protection. If a branch breaker is unable tointerrupt a short circuit fault, then an upstream breaker will open andinterrupt the fault so that the electrical circuits are protected fromdamage and igniting any fires.

The concept of selective coordination means that when a fault occursonly the circuit breaker which is immediately upstream of the fault willtrip. This limits the interruption of power to only that part of thecircuit which is experiencing a problem. This avoids a wide-spread poweroutage to other parts of the system. For example, if a fault occurs atan end load only the branch breaker of that circuit should trip and notthe main breaker. Selective coordination is highly desirable and isoften, but not always, a specified requirement for new installations.

Circuit breakers in general are devices that can stop the flow of anelectrical current under various conditions. Circuit breakers must beable to stop normal rated current when switched off. Also, they mustinterrupt overload currents, from 135% to 10 times rated current, andshort circuits up to the marked interrupting capacity of the device.

Conventional low voltage circuit breakers utilize mechanicallyseparating contacts to interrupt the flow of current. As the contactsopen, an electric arc temporarily conducts through air between thecontacts as the current is being switched off, under all conditions ofswitching off under load. The arc is inherent because whenever currentis flowing, there will be inductive energy stored in the overall circuitthat must be dissipated when the flow of current stops. The arc isresistive and produces a reverse voltage that stops the flow of current.A spring mechanism is used to open the contacts. Some circuit breakershave a blow-apart construction, in which high short circuit currentsgive rise to magnetic forces that assist in rapid contact separation,faster than can be achieved by a spring mechanism alone.

A sub-group of low voltage circuit breakers are conventional miniaturecircuit breakers (MCBs) used for small end loads such as 15-20 Acircuits or lighting loads which have been used for many years. Theseare commercially mature and low-cost devices. They typically containoverload and short-circuit trip actuators in the form of bimetals andelectromagnets, respectively. As such they are termed “thermal/magnetic”breakers. These are commonly used as branch breakers.

Even the smallest MCBs will have a short-circuit interrupting capacityof 5 or 10 kA. This amount of current typically far exceeds the normalrated current of the circuit breakers that are immediately upstream,which for example might be rated 100 or 200 A. This means a breaker thatis upstream of a MCB must be able to respond and interrupt a 5 or 10 kAfault current. But if selective coordination is a requirement, then theupstream breaker must wait without responding and allow the MCB tointerrupt the circuit if possible. But if the fault is between the MCBand the upstream breaker, or if the MCB is unable to interrupt for anyreason, then the upstream breaker must interrupt the fault.

Solid-state circuit breakers (SSCBs) that meet industry standards forlow voltage circuit breakers such as UL 489 are an emerging technology.A SSCB stops the flow of current using solid state electronics, forexample, with metal-oxide-semiconductor field-effect transistor (MOSFET)components. Like conventional arc-extinguishing circuit breakers, a SSCBproduces a reverse voltage that stops the flow of current. This reversevoltage is produced via a so-called pinching effect at the solid-statejunction. (This effect is well-known in the field of power electronics.)As with conventional breakers, there is inductive energy in the circuitthat must be dissipated when the flow of current is stopped. Unlikeconventional breakers, the energy is not dissipated via arcing; rather,it is dissipated in the electronic junction and is a function of thejunction voltage, current level, and time to reduce the current to zero.The time required to stop the current in a SSCB is extremely shorterthan an arc-extinguishing breaker. An arc-extinguishing breaker requiresfrom 2 to 16 milliseconds or greater time to extinguish, whereas a SSCBis orders of magnitude faster with time measured in nanoseconds ormicroseconds. This has two beneficial effects: (1) the short-circuit canbe stopped before the current rises to abnormally high levels, and (2)the time duration as current falls to zero is extremely short. The firstbenefit is that the inductive energy from the short circuit is muchsmaller than with an arc-extinguishing circuit breaker, because thecurrent never rises to a high level. The second benefit is that there islittle additional heat energy produced in addition to the inherentinductive energy while the current is falling to zero. As a result, aSSCB can interrupt a short circuit without any arcing at all.

On the one hand, a SSCB has excellent potential as a main or upstreambreaker. It can provide superior protection to all branch circuits. Itcan potentially eliminate damaging let-through currents. It can stop theflow of current quickly enough to reduce or eliminate arcing damage indownstream breakers. It can stop the flow of current at any point in thewaveform before it rises to a damaging level, and below the level ofcurrent that will magnetically blow apart downstream circuit breakercontacts. It can provide back-up protection for very high availablefault currents.

On the other hand, SS CBs have an inherent weakness that presents agreat difficulty for achieving selective coordination. A SSCB cannotcarry currents above its normal rated current for any sustained lengthof time. A SSCB must prevent currents from rising to high levels forself-protection. A MOSFET is unable to carry short-circuit level currentwithout being destroyed. The electronic junction is small, and it heatsvery quickly. For silicon (Si) and silicon carbide (SiC) technologies,the maximum junction temperatures are limited to about 150° C. and 600°C. respectively. Corresponding operating temperature limits in equipmentcontaining Si and SiC components are about 125° C. and 200° C.,respectively. Because of this, a SSCB must switch off when, for example,the current rises to about 5 times its normal current rating. (Thesevalues are not exact and are given only as approximate examples. Thereare multiple semiconductor technologies, and improvements are rapidlybeing made.) By contrast, the maximum short circuit current withstandcapability of conventional circuit breaker contacts is determinedprimarily by the melting points of the metals—usually silver, tungsten,and copper—which are much higher than semiconductor temperature limits.Furthermore, the contact structures are massive in comparison with asemiconductor junction. Much more heat is required to increase thetemperature of conventional breaker contacts.

But the magnetic release in a thermal/magnetic breaker requiressustained current to move the magnetic actuator. If a thermal/magneticbreaker is downstream of a SSCB and if the SSCB switches off the currentin only a few microseconds, then the thermal/magnetic breaker willremain latched. This is opposite and in contradiction to the concept ofselective coordination.

An obvious solution might be to use SSCBs as both the main and branchbreakers. However, SSCBs are many times more costly than conventionalthermal/magnetic breakers. Such a solution would be cost-prohibitive inmost cases.

Therefore, there exists a need for a means for a downstream conventionalthermal/magnetic breaker to actuate its magnetic trip device on anoverload or short circuit fault when it is being protected by anupstream SSCB.

SUMMARY

Briefly described, aspects of the present invention relate to a circuitbreaker distribution system configured to provide selectivecoordination. The invention is described in terms of a solid-statecircuit breaker (SSCB) with a continuous current rating of 100 A as mainbreaker, and a conventional miniature circuit breaker (MCB) with 20 Acontinuous current rating as the branch on a single-phase circuit. Thecircuit has system voltage of 240 VAC 60 Hz. The SSCB is programmed withlogic so that in the event of an overload or short circuit the SSCBallows repeated pulses of current through to the branch breakers. Amaximum current limit for the SSCB is chosen and defined as a “choplevel”. The chop level is chosen higher than the rated current of theSSCB, but low enough that the SSCB is not damaged from repeated pulsesover the period of time needed to trip a downstream breaker. The choplevel is high enough that the magnetic actuator in the downstreambreaker has sufficient force to actuate tripping in the downstreamdevice, but low enough that repeated momentary peaks of current do notdamage the semiconductor junctions of the SSCB. The logic of the SSCBshall be programmed so that in the event of an overcurrent conditionwhich causes the SSCB to stop the current at the chop level (500 A),repeated pulses of overload or short circuit current are subsequentlydelivered to the downstream circuit. The repeated pulses shall becontinued for a specified delay period, a preset length of time. Let usname this the “selectivity delay.” This gives the downstream MCB time totrip. After the selectivity delay is exceeded, the SSCB will shut offthe current and open, and repeated pulsing will cease. The selectivitydelay can optionally be adjustable in a SSCB user interface. If the MCBtrips during the selectivity delay, the SSCB is programmed to recognizethat the current is no longer rising to the chop level. It shall thencease to chop the current. The SSCB returns to a continuous ON state andallows current to flow to other branches downstream. Thus, selectivityis achieved, because only the MCB branch breaker has tripped and cut offcurrent to the branch circuit containing the fault. Each pulse ofcurrent that is let through the SSCB has a variable length of time. Thisis because different lengths of time are required for the current torise to the chop level. The SSCB chop criterion must be the chop level,and not a specific length of time. The SSCB chopping algorithm must beprogrammed in a way to allow the current to rise to the chop level(approximately) and then cut the current to zero. The reason for this isbecause the shape of the waveform is dependent on the phase angle of thevoltage waveform at the precise moment each pulse begins. A pulse thatbegins at 0° phase angle has a different rate of rise and shape than apulse that begins at 90°, for example. Each pulse begins at a differentvoltage phase angle, so each pulse will require a different length oftime to rise to the chop level.

In accordance with one illustrative embodiment of the present invention,a circuit breaker distribution system is configured to provide selectivecoordination. The system comprises a solid-state circuit breakerdisposed as a main or upstream breaker and a magnetic circuit breakerdisposed as a branch or downstream breaker. The solid-state circuitbreaker comprises a microcontroller including a processor and a memory,semiconductor junctions, and computer-readable logic code stored in thememory which, when executed by the processor, causes the microcontrollerto: allow repeated pulses of current through to the branch or downstreambreaker in an event of an overload or short circuit, and choose amaximum current limit for the solid-state circuit breaker as a “choplevel” such that the chop level is chosen higher than a rated current ofthe solid-state circuit breaker but low enough that the solid-statecircuit breaker is not damaged from repeated pulses over a period oftime needed to trip the branch or downstream breaker.

In accordance with one illustrative embodiment of the present invention,a method of providing selective coordination in a circuit breakerdistribution system is provided. The method comprises providing asolid-state circuit breaker disposed as a main or upstream breaker andproviding a magnetic circuit breaker disposed as a branch or downstreambreaker. The solid-state circuit breaker comprises a microcontrollerincluding a processor and a memory, semiconductor junctions, andcomputer-readable logic code stored in the memory which, when executedby the processor, causes the microcontroller to: allow repeated pulsesof current through to the branch or downstream breaker in an event of anoverload or short circuit, and choose a maximum current limit for thesolid-state circuit breaker as a “chop level” such that the chop levelis chosen higher than a rated current of the solid-state circuit breakerbut low enough that the solid-state circuit breaker is not damaged fromrepeated pulses over a period of time needed to trip the branch ordownstream breaker.

In accordance with one illustrative embodiment of the present invention,a circuit breaker distribution system is configured to provide selectivecoordination. The system comprises a solid-state switch disposed as amain or upstream breaker and a switch with an over current protectiondisposed as a branch or downstream breaker. The solid-state switchcomprises a microcontroller including a processor and a memory andcomputer-readable logic code stored in the memory which, when executedby the processor, causes the microcontroller to: allow repeated pulsesof current through to the branch or downstream breaker in an event of anoverload or short circuit, and choose a maximum current limit for thesolid-state switch as a “chop level” such that the chop level is chosenhigher than a rated current of the solid-state circuit breaker but lowenough that the solid-state switch is not damaged from repeated pulsesover a period of time needed to switch OFF the branch or downstreambreaker.

In accordance with one illustrative embodiment of the present invention,a circuit breaker distribution system is configured to provide selectivecoordination. The system comprises a solid-state switch disposed as amain or upstream breaker and a switch with an over current protectiondisposed as a branch or downstream breaker. The solid-state switchcomprises transistors that are controllable to turn ON and OFF. Thesystem further comprises a current sensing circuit or a current sensingdevice configured to turn OFF and ON the solid-state switch which allowsrepeated pulses of current through to the branch or downstream breakerin an event of an overload or short circuit and chooses a maximumcurrent limit for the solid-state switch or a “chop” level such that the“chop” level is chosen higher than a rated current of the solid-stateswitch but low enough that the solid-state switch is not damaged fromrepeated pulses over a period of time needed to switch OFF the branch ordownstream breaker.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic overview of one phase of a distribution systemthat includes a SSCB and multiple branch breakers in accordance with anexemplary embodiment of the present invention.

FIG. 2 points out specific points in the circuit where Point A is thepoint of connection of the SSCB to the power source, Point B is shortcircuit fault between the SSCB and the branch breakers and Point C is ashort circuit fault between a branch breaker and the load. in accordancewith an exemplary embodiment of the present invention

FIG. 3 shows a hypothetical short circuit waveform with 5 kA availablecurrent, 0.45 power factor, with 0° initial phase angle (a.k.a. “closingangle”) on the voltage waveform in accordance with an exemplaryembodiment of the present invention.

FIG. 4 is the same as FIG. 3 , but with a shortened time axis and theaddition of curve K.

FIG. 5 shows the chopped current and system voltage curves of FIG. 4 ,but with an expanded vertical axis in accordance with an exemplaryembodiment of the present invention.

FIG. 6 is a simplified view of a magnetic release in a typicalrepresentative MCB in accordance with an exemplary embodiment of thepresent invention.

FIG. 7 shows the magnetic torque TM that arises when current flowsthrough the MCB in accordance with an exemplary embodiment of thepresent invention.

FIG. 8 is an overview of a system simulator used to predict behavior ofa MCB downstream of a SSCB in accordance with an exemplary embodiment ofthe present invention.

FIG. 9 A-9D show example results of the system simulator of FIG. 8 inaccordance with an exemplary embodiment of the present invention.

FIGS. 10 A, 10B, 11A, 11B, 12 A, 12B, 13 A, 13B, 14 A, 14B through FIG.15 A, 15B show simulation results for circuits with progressivelyincreasing prospective currents in accordance with an exemplaryembodiment of the present invention.

FIG. 16 shows the relationship between the available current of a boltedfault and the effective available current downstream of a MCB in ourexample distribution system with SSCB as main breaker in accordance withan exemplary embodiment of the present invention.

FIG. 17 shows a summary of tripping time results in on a log-log chart,which is the format commonly used for time-current curves in accordancewith an exemplary embodiment of the present invention.

FIG. 18 shows a circuit breaker distribution system with a currentsensing circuit or a current sensing device in accordance with anexemplary embodiment of the present invention.

FIG. 19 illustrates a schematic view of a flow chart of a method ofproviding selective coordination in a circuit breaker distributionsystem in accordance with an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

To facilitate an understanding of embodiments, principles, and featuresof the present invention, they are explained hereinafter with referenceto implementation in illustrative embodiments. In particular, they aredescribed in the context of a circuit breaker distribution systemconfigured to provide selective coordination. Embodiments of the presentinvention, however, are not limited to use in the described devices ormethods.

The components and materials described hereinafter as making up thevarious embodiments are intended to be illustrative and not restrictive.Many suitable components and materials that would perform the same or asimilar function as the materials described herein are intended to beembraced within the scope of embodiments of the present invention.

These and other embodiments of the circuit breaker distribution systemaccording to the present disclosure are described below with referenceto FIGS. 1-19 herein. Like reference numerals used in the drawingsidentify similar or identical elements throughout the several views. Thedrawings are not necessarily drawn to scale.

Consistent with one embodiment of the present invention, FIG. 1represents a block diagram of one phase of a circuit breakerdistribution system 105 that includes a solid-state circuit breaker(SSCB) 107 and multiple branch breakers 110(1-10) in accordance with anexemplary embodiment of the present invention. The distribution system105 is connected to a power source 112. The power source 112 comprisesall components of an incoming power system: the generating station, anysubstations, transmission lines and transformers. For calculationpurposes, this can be reduced to an AC voltage generator 115, a sourceinductance 117 and a source resistance 120 as shown.

A simple example distribution system is shown. This is comprised of theSSCB 107 as a main breaker, which feeds a power panel 122 containingmultiple branch breakers 110(1-10) being multiple MCBs as branchbreakers. The SSCB 107 and MCBs 110(1-10) might be combined into asingle enclosure. However, it is likely that the SSCB 107 will be in aseparate enclosure, and the MCBs 110(1-10) will be mounted into aconventional panel enclosure of a type that is readily available andlow-cost. Each MCB feeds a separate branch circuit. A branch circuitwith a load 125 for one of the MCBs is shown.

The circuit breaker distribution system 105 is configured to provideselective coordination. The system 105 comprises the solid-state circuitbreaker 107 disposed as a main or upstream breaker. The system 105comprises a magnetic circuit breaker such as MCB 110(1) disposed as abranch or downstream breaker.

The solid-state circuit breaker 107 comprises a microcontroller 130including a processor 132(1) and a memory 132(2). The solid-statecircuit breaker 107 further comprises semiconductor junctions 135. Thesolid-state circuit breaker 107 further comprises computer-readablelogic code 140 stored in the memory 132(2) which, when executed by theprocessor 132(1), causes the microcontroller 130 to allow repeatedpulses 145 of current through to the branch or downstream breaker in anevent of an overload or short circuit, and choose a maximum currentlimit for the solid-state circuit breaker 107 as a “chop level” 150 suchthat the chop level 150 is chosen higher than a rated current of thesolid-state circuit breaker 107 but low enough that the solid-statecircuit breaker 107 is not damaged from the repeated pulses 145 over aperiod of time needed to trip the branch or downstream breaker.

The solid-state circuit breaker 107 is arranged in a hierarchical mannersuch that the main or upstream breaker feeds power to the branch ordownstream breaker. The branch or downstream breaker feeds power toeither end loads or to further smaller branch breakers.

In operation, when a fault occurs, only a circuit breaker which isimmediately upstream of the fault will trip thus limiting aninterruption of power to only that part of a circuit which isexperiencing a problem, for example, if a fault occurs at an end load,only the branch or downstream breaker of that circuit should trip, andnot the main or upstream breaker. In an event of an overcurrentcondition which causes the solid-state circuit breaker 107 to stop thecurrent at the chop level 150, the repeated pulses 145 of overload orshort circuit current are subsequently delivered to a downstreamcircuit. The chop level 150 is chosen high enough that a magneticactuator in the branch or downstream breaker has sufficient force toactuate tripping in a downstream device, but low enough that repeatedmomentary peaks of current do not damage the semiconductor junctions 135of the solid-state circuit breaker 107.

The repeated pulses 145 are to be continued for a specified delay periodbeing a preset length of time called a selectivity delay 155 which givesthe branch or downstream breaker time to trip. After the selectivitydelay 155 is exceeded, the solid-state circuit breaker 107 will shut OFFthe current and open such that the repeated pulses 145 will cease.

The solid-state circuit breaker 107 further comprises a user interface160 in which the selectivity delay 155 can optionally be adjustable. Ifthe branch or downstream breaker trips during the selectivity delay 155,the solid-state circuit breaker 107 is programmed to recognize that thecurrent is no longer rising to the chop level 150 so then ceases to chopthe current.

The solid-state circuit breaker 107 returns to a continuous ON state andallows current to flow to other branches downstream thus selectivity isachieved because only the branch or downstream breaker has tripped andcut off current to a branch circuit containing the fault. Each pulse ofcurrent that is let through the solid-state circuit breaker 107 has avariable length of time because different lengths of time are requiredfor the current to rise to the chop level 150 such that a solid-statecircuit breaker chop criterion is the chop level 150 and not a specificlength of time, wherein a solid-state circuit breaker chopping algorithmis programmed in a way to allow the current to rise to the chop level150 and then cut the current to zero.

The shape of a waveform is dependent on a phase angle of a voltagewaveform at a precise moment each pulse begins such that a pulse thatbegins at a 0° phase angle has a different rate of rise and shape than apulse that begins at a 90° phase angle. Each pulse begins at a differentvoltage phase angle so each pulse requires a different length of time torise to the chop level 150.

Referring to FIG. 2 , it points out specific points in a circuit 205.Point A is the point of connection of the SSCB 107 to the power source112. Point B is short circuit fault between the SSCB 107 and the branchbreakers 110(1-10). Point C is a short circuit fault between a branchbreaker 110(1) and the load 125.

Turning now to FIG. 3 , it shows a hypothetical short circuit voltagewaveform 305 with 5 kA available current, 0.45 power factor, with 0°initial phase angle (a.k.a. “closing angle”) on the voltage waveform305. Also shown are a transient DC offset 307, an available current 310,an available load current 312.

Curve D is the system voltage waveform 305 of an AC circuit. Curve E isthe available current 310 at point A of FIG. 2 . This is also known inthe industry as prospective current, or bolted fault current. It is atthis point that the UL 489 standard defines the available current. PointH is the first peak of Curve E. Point J is the 4th peak of curve E.Point H is higher than point J because of a transient DC offsetcomponent of the current, also known as the asymmetric offset. Curve Fis the transient DC offset 307. Point H is higher than J by an amountthat depends on the closing angle of the system voltage 305. Typically,0° is worst case. At best, H and J have the same height, which case isknown as symmetrical current. Curve E obeys the well-known short circuitequation:i(t)=Ip sin(ωt)+(θ−φ)−sin(θ−φ)e ^(−(R/L)(t))  (1)

where i(t) is the current at time t, Ip is peak prospective current, ωis the angular frequency in radians, θ is the initial phase closingangle of the voltage, cos(φ) is the power factor, L and R are circuitinductance and resistance, respectively.

Curve G is the reduced available current for a short circuit fault atpoint C of FIG. 2 . Curve G takes into account the inherent voltage dropacross the semiconductor junctions 135 of the SSCB 107, the resistanceof the MCB 110(1) which consists mostly of the resistance of a bimetal,and the resistance of 4 feet of cable in the load circuit. (Tests perUL489 include 4 feet of cable to represent a practical minimum.)

It is important to consider the reduction in the available current 310(per curve G) because it enhances the chopping effect. Chopped pulsesare wider and more effective if the available current is smaller. Bytaking into account the reduction in available current at the load 125,embodiments of the invention can be shown to work for a higher range ofavailable currents.

FIG. 4 is the same as FIG. 3 , but with a shortened time axis and theaddition of curve K. Curve K is a chopped current curve 405. Thisrepresents the current let through during the selectivity delay 155 by aSSCB with the chop level 150 set to 500 A. In this example the pulseinterval is set to zero. The purpose of this figure is to illustratethat the chopped current 405 magnitude may be much smaller than theavailable load current.

As seen in FIG. 5 , it shows a chopped current curve 505 and a systemvoltage curve 510 of FIG. 4 , but with an expanded vertical axis.Several characteristics of the chopped current are important:

1. Each pulse of current has a different shape. The leading edge of eachpulse is a new short-circuit waveform. Every pulse obeys equation (1).But every pulse has a different initial closing angle, and this causesthe shapes of the waveforms to vary.

2. The SSCB 107 is programmed to “chop” the current at a chop level of500 A (in this example).

3. The trailing edge of each pulse falls rapidly to zero, withinnanoseconds or a few microseconds.

4. Because of the changing initial closing angle, the pulse durationsvary.

5. Pulses have longer duration in the vicinity of the zero crossings ofthe voltage waveform 510. In the intervals 0° to 60° and 120° to 180°,pulses have longer duration than in the interval from 60° to 120°.

6. Pulses have shorter duration in the vicinity of the peaks of thevoltage waveform 510, from 60° to 120°.

Each time the current is chopped, a small amount of energy is dissipatedin the semiconductor junctions 135 as heat. It is desirable to avoidchopping the current too many times in too small a time period. Thelimiting amount of heat varies according to the construction of the SSCB107 and must be determined for a particular device.

As shown in FIG. 6 , it is a simplified view of a magnetic release in atypical representative MCB 605. The shapes of parts will vary widely inother MCB designs, however these key behaviors will be similar in manyMCBs in the market today.

When current flows through the breaker 605, a magnetic yoke 607 and amagnetic actuator 610, which are comprised of ferromagnetic steel, areattracted toward each other, causing a counterclockwise torque on theactuator 610. A latch lever 612 presses against the magnetic actuator610 resulting in friction at the latch surface. The latch friction worksagainst rotation of the magnetic actuator 610. Thus, when magnetic forceis acting, the latch friction imparts a clockwise torque to the magneticactuator 610. In addition, a return spring 615 applies clockwise torqueto the magnetic actuator 610, so that the breaker 605 can be relatchedafter tripping. A condition for tripping isT _(M)>(T _(F) +T _(S))

where T_(M) is magnetic torque, T_(F) is latch friction torque, andT_(S) is spring torque.

When this condition exists, the armature accelerates rotationallycounterclockwise, according to Newton's Law. In angular notation, thisisα=T/I=[T _(M)−(T _(F) +T _(S))]/I

Where T=T_(M)−(T_(F)+T_(S)) is the net torque on the magnetic actuator610, I is the rotational inertia of the actuator, and α is rotationalacceleration.

The magnetic armature must rotate through the entire delatch anglebefore the latch lever 612 is released and the breaker trips. This meansa certain energy must be overcome by the magnetic torque. This energy isE=(T _(F) +T _(S))θ

where θ is the delatch angle. This is significant because if E is notprovided in a single pulse, then multiple pulses will be required totrip the MCB 110(1).

In FIG. 7 , it shows the magnetic torque T_(M) that arises when currentflows through the MCB 110(1). Curves of torque versus current are shownfor various rotational positions of the magnetic actuator 610. The angleof the latched position is preset in the factory to achieve trippingaccording to the current level specified in the design.

When the MCB 110(1) is deployed in its usual way, with no SSCB in thecircuit, the magnetic actuator 610 moves when magnetic torque is higherthan the T_(F)+T_(S) line at the latched position. Then, as it movescloser to the yoke 607, the magnetic forces become generally stronger.But the applied current also is constantly changing. Therefore, themagnetic force is a function of both the changing current and theactuator position.

When the MCB 110(1) is applied as a downstream breaker from a SSCBaccording to the present invention, then the chop level 150 becomesrelevant. The applied current will always be less than the chop level150, which is 500 A in the example.

With regard to FIG. 8 , it is an overview of a system simulator 805 usedto predict behavior of a MCB 110(1) downstream of a SSCB such as 107.Via computation, it was determined how the MCB 110(1) would respond tochopped current let through by the SSCB 107, under a variety ofscenarios.

With respect to FIGS. 9A-9D, they show example results of the systemsimulator 805 of FIG. 8 . FIG. 9A shows current below the chop level150, so it is sinusoidal. A phase closing angle has been selected toproduce a symmetric sinusoid. FIG. 9B shows the magnetic actuator motion(solid line) of the MCB 110(1) from the current in FIG. 9A. Magneticforce is insufficient to move the actuator 610. FIG. 9C shows currentjust below the chop level 150. FIG. 9D shows magnetic actuator motion(solid line) from the current in FIG. 9C. This figure shows that the MCB110(1) trips. The long-dashed line is the unlatching point of theactuator 610. The short-dashed line is where the actuator 610 strikesagainst the magnetic yoke 607 and stops.

In the following FIGS. 10A, 10B, 11A, 11B, 12A, 12B, 13A, 13B, 14A, 14Bthrough FIG. 15A, 15B, simulation results are shown for circuits withprogressively increasing prospective currents. In each of these cases,for consistency, phase closing angles are chosen to achieve symmetriccurrents. In general, if worst case asymmetric closing angles werechosen, results would be similar, except that chopping would occur atsmaller prospective currents. These simulations do not include any pulseinterval. For the higher prospective currents 2000 to 10000 A, thechopped current in the figures appears to not chop to zero nor reach 500A. This is only an illusion, because not every point of the simulationis plotted. The simulations often had over 1 million time steps, andthis was too many to plot in Excel software. These simulations show thatwith chopped current, the MCB 110(1) can be caused to trip over a rangeof prospective from its normal threshold all the way to 10 kA.

FIG. 16 shows the relationship between an available current 1605 of abolted fault and the effective available current downstream of the MCB110(1) in our example distribution system with the SSCB 107 as mainbreaker. When circuit breakers are tested in a high power testlaboratory according to UL489, the actual current that flows through thebreaker is significantly less than value of the nominal calibratedcircuit. This is because circuits are calibrated with a bolted shortingbar. But actual short circuit tests of a circuit breaker includeadditional resistance. In this chart, additional resistance was added tothe circuit to account for resistance across the SSCB 107 semiconductorjunctions 135, the resistance of a bimetal in the MCB 110(1), and 4 feetof #12 AWG cable. Likewise, the additional resistance increases aneffective power factor 1610 at the breaker load, as shown in the chart.Also see a power factor 1615 per UL Std in the chart.

The significance of this chart is that it extends the usable range ofselectivity of the present invention. For example, it was demonstratedthat with 6937 A available current at the breaker load, the MCB 110(1)can be made to trip on chopped current with a chopping level of 500 A,this means that selectivity is achieved for a 10,000 A available boltedfault current. It can then be claimed that selectivity is achieved for a10 kA circuit.

FIG. 17 shows a summary of tripping time results in on a log-log chart,which is the format commonly used for time-current curves. But in thiscase, only the parts of the tripping curve are shown for the magneticrelease. Tripping from the thermal release (bimetal) at lower currentsand longer times is not shown.

The x-axis shows actual RMS current through the MCB 110(1), not theprospective current of a bolted fault. In these simulations asymmetrical current was used. In each case, a voltage phase closingangle was chosen that produced symmetrical current. The relationshipbetween prospective current and resulting current through the MCB 110(1)is shown in FIG. 16 .

A long-dashed line 1705 represents a MCB acting alone, without anycurrent chopping from an upstream SSCB. It follows the usualinverse-time/current relationship that is expected of a thermal/magneticcircuit breaker.

The other three curves show the time/current relationship that can beexpected of a MCB subjected to chopped current according to thedifferent variations of the present invention. It is a positive sloperelationship. As the available current increases, the individual pulsesof chopped current become shorter in duration, and more pulses arerequired to move the MCB magnetic actuator 610 and overcome latchfriction.

The advantages arise from using a SSCB as an upstream breaker in aselectivity system.

Even when the downstream breaker trips on chopped current, very littlelet-through energy reaches the load 125. The current never rises abovethe chop level 150. In our example system, on a 5 kA prospective shortcircuit, the MCB 110(1) would see no more than 500 A. Whereas, the sameMCB in a conventional distribution system would see a peak current ofnearly 6000 A.

There will be little arcing in the downstream breaker from shortcircuits, regardless of the level of prospective current. There will besome arcing from routine ON/OFF operations at normal load current andlow-level overloads, so the breaker must meet its conventional loadendurance and overload operations capability. However, the downstreambreaker will no longer be subjected to damaging high short circuitcurrents. Typically, electrical contacts must be sized to withstanderosion from the worst short circuit currents. A high-level shortcircuit significantly reduces the life of the electrical contacts. Butwith an SSCB upstream, the life and reliability of conventional circuitbreakers will be extended. The need for maintenance or replacement ofbreakers after short circuit events will be greatly reduced.

Even though the downstream MCB 110(1) carries a 5 to 10 kA interruptionrating, the interrupting ability of the downstream device is no longerneeded, except to meet standards that were developed for technologyprior to SSCBs. In the future, lower cost downstream devices can bedeveloped for use in selective distribution systems. For example, thearc plate assemblies might be omitted, contact breaking distancesreduced, and simpler spring mechanisms used.

The following statements define a set-up for the present invention:

1. There is a SSCB.

2. The SSCB provides overcurrent protection by use of a power electroniccomponent that stops the flow of current.

3. The SSCB and a second switching device are wired in series.

4. The SSCB is upstream—electrically nearer the power source—and thesecond switching device is downstream—electrically nearer the load.

5. The second switching device has a magnetic overcurrent release and itmay have other types of releases.

6. The magnetic release of the second switching device has maximumovercurrent tripping ability that is greater than the continuous currentrating of the SSCB.

7. The SSCB is able to allow current to flow momentarily up to a choplevel that is higher than the current rating of the second switchingdevice.

8. The chop level is higher than the minimum current needed to causemotion of the magnetic actuator of the second switching device.

9. In an overcurrent situation, the SSCB passes repeated pulses ofcurrent, if the overcurrent exceeds the chop level.

10. In an overcurrent situation, the SSCB protects itself by choppingthe repeated current pulses to zero, whenever the current rises to thechop level.

11. In some overcurrent situations, when the fault is downstream of thesecond switching device, the repeated pulses passed by the SSCB willeventually cause the second switching device to trip.

FIG. 18 shows a circuit breaker distribution system 1805 with a currentsensor 1807 (e.g., a current sensing circuit or a current sensingdevice). FIG. 18 shows a, b, and c as alternate locations for thecurrent sensor 1807. The circuit breaker distribution system 1805 isconfigured to provide selective coordination. The system comprises asolid-state switch 1810 (e.g., a SSCB) disposed as a main or upstreambreaker and a switch with an over current protection 1815(1) (e.g., aMCB) disposed as a branch or downstream breaker. The solid-state switch1810 comprises transistors 1820 that are controllable to turn ON andOFF. The system further comprises the current sensor 1807 (e.g., acurrent sensing circuit or a current sensing device) that is configuredto turn OFF and ON the solid-state switch 1810 which allows repeatedpulses of current through to the branch or downstream breaker in anevent of an overload or short circuit and chooses a maximum currentlimit for the solid-state switch 1810 or a “chop” level such that the“chop” level is chosen higher than a rated current of the solid-stateswitch 1810 but low enough that the solid-state switch 1810 is notdamaged from repeated pulses over a period of time needed to switch OFFthe branch or downstream breaker.

The solid-state switch 1810 further comprises a microcontrollerincluding a processor and a memory and computer-readable logic codestored in the memory which, when executed by the processor, causes themicrocontroller to: allow repeated pulses of current through to thebranch or downstream breaker in an event of an overload or shortcircuit, and choose a maximum current limit for the solid-state switchor a “chop” level such that the “chop” level is chosen higher than arated current of the solid-state switch but low enough that thesolid-state switch is not damaged from repeated pulses over a period oftime needed to switch OFF the branch or downstream breaker.

It is intended that the present invention may be applied not only in ACdistribution systems, but also in DC distribution systems. Clearly,repeated pulses of current, limited by a chop level, may be used to tripa downstream breaker in DC applications also. In both cases, the choplevel is chosen higher than a rated current of the SSCB, higher than thecurrent necessary to move the magnetic armature of the downstreambreaker, and low enough that the SSCB is not damaged.

In fact, the present invention may in some situations provide anadvantage in DC cases for tripping a downstream breaker. Often, magnetictripping devices benefit from the repeated vibrations caused by ACcurrent. The repeated vibrations sometimes assist in causing the deviceto unlatch. But in DC applications, the magnetic armature experiencesonly one application of the force. Sometimes this does not produceenough motion to unlatch the breaker. In such cases the breaker might beassigned a different trip rating than AC, or the DC version of thebreaker might have a different construction than the AC version. But therepeated pulses of the present invention might produce tripping behaviorin DC applications similar to AC applications, thus improvingconsistency and reducing the need for rerating or special constructions.

Whereas it was stated that for AC applications the present inventionwill have pulses of varying rate-of-rise and time duration, this is notthe case in DC applications. Since rate-of-rise and pulse time durationdepend on the instantaneous value of the system voltage, and for DCapplications the system voltage is constant, then in DC applications thepresent invention will have non-variable repeating pulses, all withidentical rate-of-rise and time duration.

In DC applications, it may still be beneficial to add a pulse interval.The pulse interval will reduce the heating in the electronic switchingcomponents.

FIG. 19 illustrates a schematic view of a flow chart of a method 1900 ofproviding selective coordination in the circuit breaker distributionsystem 105 in accordance with an exemplary embodiment of the presentinvention. Reference is made to the elements and features described inFIGS. 1-18 . It should be appreciated that some steps are not requiredto be performed in any particular order, and that some steps areoptional.

The method 1900 comprises a step 1905 of providing a solid-state circuitbreaker disposed as a main or upstream breaker. The method 1900 furthercomprises a step 1910 of providing a magnetic circuit breaker disposedas a branch or downstream breaker. The solid-state circuit breakercomprises a microcontroller including a processor and a memory,semiconductor junctions, and computer-readable logic code stored in thememory which, when executed by the processor, causes the microcontrollerto: allow repeated pulses of current through to the branch or downstreambreaker in an event of an overload or short circuit, and choose amaximum current limit for the solid-state circuit breaker as a “choplevel” such that the chop level is chosen higher than a rated current ofthe solid-state circuit breaker but low enough that the solid-statecircuit breaker is not damaged from repeated pulses over a period oftime needed to trip the branch or downstream breaker.

A circuit breaker distribution system is configured to provide selectivecoordination such that the system comprises a solid-state switchdisposed as a main or upstream breaker and a switch with an over currentprotection disposed as a branch or downstream breaker. The solid-stateswitch comprises a microcontroller including a processor and a memory,and computer-readable logic code stored in the memory which, whenexecuted by the processor, causes the microcontroller to: allow repeatedpulses of current through to the branch or downstream breaker in anevent of an overload or short circuit, and choose a maximum currentlimit for the solid-state switch as a “chop level” such that the choplevel is chosen higher than a rated current of the solid-state circuitbreaker but low enough that the solid-state switch is not damaged fromrepeated pulses over a period of time needed to switch OFF the branch ordownstream breaker.

While a circuit breaker distribution system for a SSCB and a MCB isdescribed here a range of one or more other breakers or other forms ofbreakers are also contemplated by the present invention. For example,other types of breakers may be implemented based on one or more featurespresented above without deviating from the spirit of the presentinvention.

The techniques described herein can be particularly useful for a logicof the SSCB that is to be programmed. While particular embodiments aredescribed in terms of a logic of the SSCB that is to be programmed, thetechniques described herein are not limited to such a set-up but canalso be used with other set-ups.

While embodiments of the present invention have been disclosed inexemplary forms, it will be apparent to those skilled in the art thatmany modifications, additions, and deletions can be made therein withoutdeparting from the spirit and scope of the invention and itsequivalents, as set forth in the following claims.

Embodiments and the various features and advantageous details thereofare explained more fully with reference to the non-limiting embodimentsthat are illustrated in the accompanying drawings and detailed in thefollowing description. Descriptions of well-known starting materials,processing techniques, components and equipment are omitted so as not tounnecessarily obscure embodiments in detail. It should be understood,however, that the detailed description and the specific examples, whileindicating preferred embodiments, are given by way of illustration onlyand not by way of limitation. Various substitutions, modifications,additions and/or rearrangements within the spirit and/or scope of theunderlying inventive concept will become apparent to those skilled inthe art from this disclosure.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, article, orapparatus.

Additionally, any examples or illustrations given herein are not to beregarded in any way as restrictions on, limits to, or expressdefinitions of, any term or terms with which they are utilized. Instead,these examples or illustrations are to be regarded as being describedwith respect to one particular embodiment and as illustrative only.Those of ordinary skill in the art will appreciate that any term orterms with which these examples or illustrations are utilized willencompass other embodiments which may or may not be given therewith orelsewhere in the specification and all such embodiments are intended tobe included within the scope of that term or terms.

In the foregoing specification, the invention has been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention. Accordingly, thespecification and figures are to be regarded in an illustrative ratherthan a restrictive sense, and all such modifications are intended to beincluded within the scope of invention.

Although the invention has been described with respect to specificembodiments thereof, these embodiments are merely illustrative, and notrestrictive of the invention. The description herein of illustratedembodiments of the invention is not intended to be exhaustive or tolimit the invention to the precise forms disclosed herein (and inparticular, the inclusion of any particular embodiment, feature orfunction is not intended to limit the scope of the invention to suchembodiment, feature or function). Rather, the description is intended todescribe illustrative embodiments, features and functions in order toprovide a person of ordinary skill in the art context to understand theinvention without limiting the invention to any particularly describedembodiment, feature or function. While specific embodiments of, andexamples for, the invention are described herein for illustrativepurposes only, various equivalent modifications are possible within thespirit and scope of the invention, as those skilled in the relevant artwill recognize and appreciate. As indicated, these modifications may bemade to the invention in light of the foregoing description ofillustrated embodiments of the invention and are to be included withinthe spirit and scope of the invention. Thus, while the invention hasbeen described herein with reference to particular embodiments thereof,a latitude of modification, various changes and substitutions areintended in the foregoing disclosures, and it will be appreciated thatin some instances some features of embodiments of the invention will beemployed without a corresponding use of other features without departingfrom the scope and spirit of the invention as set forth. Therefore, manymodifications may be made to adapt a particular situation or material tothe essential scope and spirit of the invention.

Respective appearances of the phrases “in one embodiment,” “in anembodiment,” or “in a specific embodiment” or similar terminology invarious places throughout this specification are not necessarilyreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics of any particular embodiment may becombined in any suitable manner with one or more other embodiments. Itis to be understood that other variations and modifications of theembodiments described and illustrated herein are possible in light ofthe teachings herein and are to be considered as part of the spirit andscope of the invention.

In the description herein, numerous specific details are provided, suchas examples of components and/or methods, to provide a thoroughunderstanding of embodiments of the invention. One skilled in therelevant art will recognize, however, that an embodiment may be able tobe practiced without one or more of the specific details, or with otherapparatus, systems, assemblies, methods, components, materials, parts,and/or the like. In other instances, well-known structures, components,systems, materials, or operations are not specifically shown ordescribed in detail to avoid obscuring aspects of embodiments of theinvention. While the invention may be illustrated by using a particularembodiment, this is not and does not limit the invention to anyparticular embodiment and a person of ordinary skill in the art willrecognize that additional embodiments are readily understandable and area part of this invention.

It will also be appreciated that one or more of the elements depicted inthe drawings/figures can also be implemented in a more separated orintegrated manner, or even removed or rendered as inoperable in certaincases, as is useful in accordance with a particular application.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any component(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or component.

What is claimed is:
 1. A circuit breaker distribution system configuredto provide selective coordination, the system comprising: a solid-statecircuit breaker disposed as a main or upstream breaker; and a magneticcircuit breaker disposed as a branch or downstream breaker, wherein themagnetic circuit breaker comprising a magnetic trip element andseparable mechanical contacts, and wherein the solid-state circuitbreaker comprises a microcontroller including a processor and a memory,semiconductor junctions, and computer-readable logic code stored in thememory which, when executed by the processor, causes the microcontrollerto: allow repeated pulses of current through to the branch or downstreambreaker in an event of an overload or short circuit, and choose amaximum current limit, that is, a maximum peak current of each currentpulse of the repeated pulses of current, for the solid-state circuitbreaker as a “chop level” such that the chop level is chosen higher thana rated current of the solid-state circuit breaker but low enough thatthe solid-state circuit breaker is not damaged from repeated pulses overa period of time needed to trip the branch or downstream breaker,wherein the maximum peak current is the same for each current pulse. 2.The circuit breaker distribution system of claim 1, wherein thesolid-state circuit breaker is arranged in a hierarchical manner suchthat the main or upstream breaker feeds power to the branch ordownstream breaker, wherein the branch or downstream breaker feeds powerto either end loads or to further smaller branch breakers, wherein whena fault occurs, only a circuit breaker which is immediately upstream ofthe fault will trip thus limiting an interruption of power to only thatpart of a circuit which is experiencing a problem such that if a faultoccurs at an end load, only the branch or downstream breaker of thatcircuit should trip, and not the main or upstream breaker, wherein in anevent of an overcurrent condition which causes the solid-state circuitbreaker to stop the current at the chop level, the repeated pulses ofoverload or short circuit current are subsequently delivered to adownstream circuit, and wherein the chop level is chosen high enoughthat a magnetic actuator in the branch or downstream breaker hassufficient force to actuate tripping in a downstream device, but lowenough that repeated momentary peaks of current do not damage thesemiconductor junctions of the solid-state circuit breaker.
 3. Thecircuit breaker distribution system of claim 2, wherein the repeatedpulses are to be continued for a specified delay period being a presetlength of time called a selectivity delay which gives the branch ordownstream breaker time to trip.
 4. The circuit breaker distributionsystem of claim 3, wherein after the selectivity delay is exceeded, thesolid-state circuit breaker will shut OFF the current and open such thatthe repeated pulses will cease.
 5. The circuit breaker distributionsystem of claim 4, wherein the solid-state circuit breaker comprising: auser interface in which the selectivity delay can optionally beadjustable.
 6. The circuit breaker distribution system of claim 5,wherein if the branch or downstream breaker trips during the selectivitydelay, the solid-state circuit breaker is programmed to recognize thatthe current is no longer rising to the chop level so then ceases to chopthe current.
 7. The circuit breaker distribution system of claim 6,wherein the solid-state circuit breaker returns to a continuous ON stateand allows current to flow to other branches downstream thus selectivityis achieved because only the branch or downstream breaker has trippedand cut off current to a branch circuit containing the fault.
 8. Thecircuit breaker distribution system of claim 1, wherein each pulse ofcurrent that is let through the solid-state circuit breaker has avariable length of time because different lengths of time are requiredfor the current to rise to the chop level such that a solid-statecircuit breaker chop criterion is the chop level and not a specificlength of time, wherein a solid-state circuit breaker chopping algorithmis programmed in a way to allow the current to rise to the chop leveland then cut the current to zero.
 9. The circuit breaker distributionsystem of claim 8, wherein shape of a waveform is dependent on a phaseangle of a voltage waveform at a precise moment each pulse begins suchthat a pulse that begins at a 0° phase angle has a different rate ofrise and shape than a pulse that begins at a 90° phase angle.
 10. Thecircuit breaker distribution system of claim 9, wherein each pulsebegins at a different voltage phase angle so each pulse requires adifferent length of time to rise to the chop level.
 11. A method ofproviding selective coordination in a circuit breaker distributionsystem, the method comprising: providing a solid-state circuit breakerdisposed as a main or upstream breaker; and providing a magnetic circuitbreaker disposed as a branch or downstream breaker, wherein the magneticcircuit breaker comprising a magnetic trip element and separablemechanical contacts, wherein the solid-state circuit breaker comprises amicrocontroller including a processor and a memory, semiconductorjunctions, and computer-readable logic code stored in the memory which,when executed by the processor, causes the microcontroller to: allowrepeated pulses of current through to the branch or downstream breakerin an event of an overload or short circuit, and choose a maximumcurrent limit, that is, a maximum peak current of each current pulse ofthe repeated pulses of current, for the solid-state circuit breaker as a“chop level” such that the chop level is chosen higher than a ratedcurrent of the solid-state circuit breaker but low enough that thesolid-state circuit breaker is not damaged from repeated pulses over aperiod of time needed to trip the branch or downstream breaker, whereinthe maximum peak current is the same for each current pulse.
 12. Themethod of claim 11, wherein the solid-state circuit breaker is arrangedin a hierarchical manner such that the main or upstream breaker feedspower to the branch or downstream breaker, wherein the branch ordownstream breaker feeds power to either end loads or to further smallerbranch breakers, wherein when a fault occurs, only a circuit breakerwhich is immediately upstream of the fault will trip thus limiting aninterruption of power to only that part of a circuit which isexperiencing a problem such that if a fault occurs at an end load, onlythe branch or downstream breaker of that circuit should trip, and notthe main or upstream breaker, wherein in an event of an overcurrentcondition which causes the solid-state circuit breaker to stop thecurrent at the chop level, the repeated pulses of overload or shortcircuit current are subsequently delivered to a downstream circuit, andwherein the chop level is chosen high enough that a magnetic actuator inthe branch or downstream breaker has sufficient force to actuatetripping in a downstream device, but low enough that repeated momentarypeaks of current do not damage the semiconductor junctions of thesolid-state circuit breaker.
 13. The method of claim 12, wherein therepeated pulses are to be continued for a specified delay period being apreset length of time called a selectivity delay which gives the branchor downstream breaker time to trip.
 14. The method of claim 13, whereinafter the selectivity delay is exceeded, the solid-state circuit breakerwill shut OFF the current and open such that the repeated pulses willcease.
 15. The method of claim 14, wherein the solid-state circuitbreaker comprising: a user interface in which the selectivity delay canoptionally be adjustable.
 16. The method of claim 15, wherein if thebranch or downstream breaker trips during the selectivity delay, thesolid-state circuit breaker is programmed to recognize that the currentis no longer rising to the chop level so then ceases to chop thecurrent.
 17. The method of claim 16, wherein the solid-state circuitbreaker returns to a continuous ON state and allows current to flow toother branches downstream thus selectivity is achieved because only thebranch or downstream breaker has tripped and cut off current to a branchcircuit containing the fault.
 18. The method of claim 11, wherein eachpulse of current that is let through the solid-state circuit breaker hasa variable length of time because different lengths of time are requiredfor the current to rise to the chop level such that a solid-statecircuit breaker chop criterion is the chop level and not a specificlength of time, wherein a solid-state circuit breaker chopping algorithmis programmed in a way to allow the current to rise to the chop leveland then cut the current to zero.
 19. The method of claim 18, whereinshape of a waveform is dependent on a phase angle of a voltage waveformat a precise moment each pulse begins such that a pulse that begins at a0° phase angle has a different rate of rise and shape than a pulse thatbegins at a 90° phase angle.
 20. The method of claim 19, wherein eachpulse begins at a different voltage phase angle so each pulse requires adifferent length of time to rise to the chop level.
 21. A circuitbreaker distribution system configured to provide selectivecoordination, the system comprising: a solid-state switch disposed as amain or upstream breaker; and a switch with an over current protectiondisposed as a branch or downstream breaker, wherein the over currentprotection comprises a magnetic trip element, wherein the solid-stateswitch comprises a microcontroller including a processor and a memory,and computer-readable logic code stored in the memory which, whenexecuted by the processor, causes the microcontroller to: allow repeatedpulses of current through to the branch or downstream breaker in anevent of an overload or short circuit, and choose a maximum currentlimit, that is, a maximum peak current of each current pulse of therepeated pulses of current, for the solid-state switch as a “chop level”such that the chop level is chosen higher than a rated current of thesolid-state switch circuit breaker but low enough that the solid-stateswitch is not damaged from repeated pulses over a period of time neededto switch OFF the branch or downstream breaker, wherein the maximum peakcurrent is the same for each current pulse.
 22. A circuit breakerdistribution system configured to provide selective coordination, thesystem comprising: a solid-state switch disposed as a main or upstreambreaker; a switch with an over current protection disposed as a branchor downstream breaker wherein the over current protection comprises amagnetic trip element, wherein the solid-state switch comprisestransistors that are controllable to turn ON and OFF; and a currentsensing circuit or a current sensing device configured to turn OFF andON the solid-state switch which allows repeated pulses of currentthrough to the branch or downstream breaker in an event of an overloador short circuit and chooses a maximum current limit, that is, a maximumpeak current of each current pulse of the repeated pulses of current,for the solid-state switch or a “chop” level such that the “chop” levelis chosen higher than a rated current of the solid-state switch but lowenough that the solid-state switch is not damaged from repeated pulsesover a period of time needed to switch OFF the branch or downstreambreaker, wherein the maximum peak current is the same for each currentpulse.
 23. The system of claim 22, wherein the solid-state switchfurther comprises a microcontroller including a processor and a memoryand computer-readable logic code stored in the memory which, whenexecuted by the processor, causes the microcontroller to: allow repeatedpulses of current through to the branch or downstream breaker in anevent of an overload or short circuit, and choose a maximum currentlimit for the solid-state switch or a “chop” level such that the “chop”level is chosen higher than a rated current of the solid-state switchbut low enough that the solid-state switch is not damaged from repeatedpulses over a period of time needed to switch OFF the branch ordownstream breaker.